Another factor to the same end is that the denser bands of late wood are continuous in a tangential direction, while radially they are separated by alternate zones of less dense early wood.

Consequently the shrinkage along the rings (tangential) is fully twice as much as toward the centre (radial).

(See Table XIV.) This explains why some cracks open more and more as drying advances.

(See Fig.
27.) Although actual shrinkage in length is small, nevertheless the tendency of the rays to shorten a stick produces strains which are responsible for some of the splitting open of ties, posts, and sawed timbers with box heart.

At the very centre of a tree the wood is light and weak, while farther out it becomes denser and stronger.